Morphometric relations and diet compositions of Nile tilapia Oreochromis niloticus (Linn. 1758) in Lake Tana Gorgora gulf, Ethiopia

Abstract

Oreochromis niloticus is the most ecologically and economically important fish in tropical and sub-tropical aquatic systems. Recently, due to sever anthropogenic stressors, hydrological variations and infestations of invasive alien species in Ethiopian water bodies, fish community structure and ecosystem of Lake Tana is changing alarmingly. So far, there is paucity of information on the morphometric relations and diet composition of O. niloticus in Lake Tana, gulf of Gorgora. A total of 309 fish samples were collected and their total length (TL), standard length (SL) and total weight (TW) were measured to determine morphometric relations; and gut contents were examined to identify most important food item in the diet of the fish. Results indicated that, the relation between TL and SL was significant (p < 0.001) and linear (SL = 0.942TL-2.41) while the relation between TL and TW was curvilinear (TW = 0.014 TL 2.8 ) indicating allometric growth. Among the total guts scrutinized, 53 (17.3%) of them were empty and the remaining 256 (82.7%) were non-empty. Phytoplankton constituted the largest bulk and occurred in 77% of the guts examined and volumetrically accounted 44.3%. Detritus and zooplankton had an intermediate importance by occurring 60.2% and 63.3% of all guts scrutinized and constituted about 25.6% and 15.5% of the total volume respectively. Contributions of macrophytes, insects, nematodes and unidentified food items were relatively low in their importance. Ontogenetic dietary shift was observed in the diet indicating an omnivorous feeding habit of the adult fish.

Food and Feeding Habits of Oreochromis Niloticus in Lower River Benue, Makurdi

“…The stomach content analysis of O. niloticus suggests that it is primarily an herbivorous fish that feeds on plant-based food items such as green algae, plant tissues, and plant seeds, as well as detritus. Herbivorous feeding habits of O. niloticus have also been reported in Ethiopian water bodies such as Lake Chamo (Teferi et al, 2000), Koka Reservoir (Engdaw et al, 2013) and Lake Hayq (Assefa and Getahun, 2015). However, this result was in disagreement with Oso et al (2006), who suggested that O. niloticus has omnivorous feeding habits.…”

“…This high stomach vacuity index may be attributed the post-harvest digestion or the method of catching of the specimens. Engdaw et al (2013) also reported an empty stomach for O. niloticus, caught with gill nets in Ero and Koka reservoir. The reason for this may be due to the fact that the food items in their stomach may have been regurgitated or digested as the fish struggled for escape in gill nets during the catches.…”